The present invention relates to improvements in dot-matrix luminous displays constructed of luminous elements such as light-emitting diodes.
Luminous displays of this type are designed to display desired characters, symbols or patterns in the form of a dot pattern by supplying power to and lighting selected luminous elements arranged in a matrix.
The basic structure of such a matrix display includes upper and lower electrodes arranged in a three-dimensional matrix with an insulating layer sandwiched therebetween, and semiconductor chips disposed at intersections between the upper and lower electrodes.
Referring to FIGS. 1 and 2, the general structure of such a matrix display will be described. Two sheets of insulating substrates 102 and 103, respectively bearing parallel rows of upper electrodes 100 and lower electrodes 101 on their surfaces, are coupled together to form a matrix luminous display board (hereinafter referred to as simply a "matrix board" or "display board") 1 with the upper and lower electrodes 100 and 101 arranged in a three-dimensional matrix. There are provided through-holes 104 in portions where the upper and lower electrodes 100 and 101 intersect. A semiconductor chip 105, forming a single luminous element, is supplied in each through-hole 104, and, as a final process, the entire surface of the matrix board 1, including the through-holes 104 through which are exposed the semiconductor chips 105, is coated with a translucent thermosetting resin to provide thereby a continuous protective film 107. In addition, bonding wires 106 are used to connect the semiconductor chips 105 to the upper electrodes 100, whereas solder or silver paste 108 is used to provide conductive connection between the bottoms of the semiconductor chips 105 and the lower electrodes 101.
Typically, the spacing between outer edges of adjacent through-holes 104 is about 8.0 mm, the diameter of each through-hole 104 is about 6.5 mm, and the length of a side of the display board 1, is about 64 mm. However, during the process of manufacturing such matrix boards, specifically, when the boards are coated with the translucent thermosetting resin film 107, there may be produced strain, camber, peeling and cracks (hereinafter collectively referred to as "flaws such as strains") at the joints of the matrix board 1 and the protective film 107 because of the difference therebetween in the coefficient of thermal expansion. These flaws such as strains result in defective products.
Moreover, the flaws such as strains become more pronounced as the size of the matrix board 1 is increased. Even finished products are not free from such strains caused by, for instance, the temperature difference between summer and winter or heat generated when power is supplied to the luminous elements.